The present invention relates to a program and method used to determine a position of an object, such a vehicle, that moves in a geographic region represented by a geographic database, and more particularly, the present invention relates to a program and method used in a navigation system installed in a vehicle to determine in real time a position of the vehicle relative to geographic data used by the navigation system.
In-vehicle navigation systems provide a variety of useful features to end users (i.e., the drivers and/or passengers of the vehicles in which the navigation systems are installed). Included among the features that are provided by some in-vehicle navigation systems are route calculation, route guidance, emergency roadside services, electronic yellow pages, and so on. In order to provide these kinds of features, in-vehicle navigation systems use geographic data. The geographic data may be stored in the vehicle in which the in-vehicle navigation system is installed or alternatively, some or all of the geographic data may be stored remotely and made available to the navigation system in the vehicle through a wireless communication system which may be part of the navigation system. The geographic data include information about features in a covered geographic region. The geographic data includes information about the location of roads, the speed limits along roads, turn restrictions at intersections, the names of roads, the address ranges along roads, the locations of points of interest, and so on.
Some of the features provided by in-vehicle navigation systems require that the position of the vehicle be determined. There are several considerations related to determining the position of the vehicle. For example, a GPS system may be used to obtain the geographic coordinates of the vehicle. However, the geographic coordinates only indicate the position of the vehicle relative to the surface of the earth. For some of the features provided by in-vehicle navigation systems, a means is required to determine the vehicle position relative to the road network which is represented by the geographic data used by the in-vehicle navigation system. In other words, if the vehicle is located on a road segment, a means is required to identify the road segment, and optionally the position and direction along the road segment. Once the vehicle position is determined relative to the road segments in the geographic area, programming in the in-vehicle navigation system can be used to provide various features, such as determining a route to a desired destination, providing maneuvering instructions for reaching the destination, identifying the closest restaurant or gas station relative to the vehicle position, displaying a map of the area around the vehicle, and so on.
Some of the features provided by in-vehicle navigation systems require that the vehicle position be updated continuously in real time as the vehicle is driven along roads in a geographic region. For example, in some navigation systems, a map display feature may continuously update a graphic display of a map of the area through which the vehicle is traveling on a display of the navigation system. Also, a route guidance function provided by some navigation systems may provide maneuvering instructions to the driver as the vehicle approaches the location at which the maneuver is required. These kinds of functions require that the data identifying the vehicle position be updated continuously or regularly as the vehicle moves in a geographic region.
There are prior methods for determining a vehicle position relative to the data in a geographic database. However, a need for an improved method continues to exist. For example, there is a need to determine a vehicle position relative to data in a geographic database with greater precision and accuracy than can be provided by some prior methods. Also, there is a need to determine a vehicle position relative to the data in a geographic database with a more efficient use of the computing resources of the in-vehicle navigation system. Accordingly, there is a need for an improved vehicle positioning program and method.